The present invention generally relates to printing technology, and more particularly involves an improved, high-durability printhead system for use in an ink cartridge (e.g. a thermal inkjet system).
Substantial developments have been made in the field of electronic printing technology. Specifically, a wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing systems using thermal inkjet technology basically involve a cartridge which includes at least one ink reservoir chamber in fluid communication with a substrate having a plurality of resistors thereon. Selective activation of the resistors causes thermal excitation of the ink and expulsion of the ink from the cartridge. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. pat. No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
In order to effectively deliver ink materials to a selected substrate, thermal inkjet printheads typically include an outer plate member known as an "orifice plate" or "nozzle plate" which includes a plurality of ink ejection orifices (e.g. openings) therethrough. Initially, these orifice plates were manufactured from one or more metallic compositions including but not limited to gold-plated nickel and similar materials. However, recent developments in thermal inkjet printhead design have resulted in the production of orifice plates which are non-metallic in character, with the term "non-metallic" being defined to involve one or more material layers which are devoid of elemental metals, metal amalgams, or metal alloys. In a preferred embodiment, these non-metallic orifice plates are produced from a variety of different organic polymers including but not limited to film products consisting of polytetrafluoroethylene (e.g. Teflon.RTM.), non-thermoplastic polyimide, polymethylmethacrylate, polycarbonate, polyester, polyamide, polyethyleneterephthalate, and mixtures thereof. A representative polymeric (e.g. non-thermoplastic polyimide-based) composition which is suitable for this purpose is a commercial product sold under the trademark "KAPTON" by E.I. DuPont de Nemours and Company of Wilmington, Del. (USA). Orifice plate structures produced from the non-metallic compositions described above are typically uniform in thickness, with an average thickness range of about 1.0-2.0 mil. Likewise, they provide numerous benefits ranging from reduced production costs to a substantial simplification of the printhead structure which translates into improved reliability, economy, and ease of manufacture. The fabrication of film-type, non-metallic orifice plates and the corresponding production of the entire printhead structure is typically accomplished using conventional tape automated bonding ("TAB") technology as generally discussed in U.S. Pat. No. 4,944,850 to Dion. Likewise, further detailed information regarding polymeric, non-metallic orifice plates of the type described above is discussed in the following U.S. patents: U.S. Pat. No. 5,278,584 to Keefe et al. and No. 5,305,015 to Schantz et al.
However, a primary consideration in the selection of any materials to be used in the production of an ink cartridge printhead is the overall durability of the completed structure. The term "durability" as used herein shall encompass a wide variety of characteristics including but not limited to stability over a wide range of temperatures, as well as resistance to the "solvent effects" caused by many ink compositions. Regarding solvent resistance, typical ink compositions include one or more solvents which can cause degradation, deterioration, and/or separation of the various printhead structures in the system described above. As a result, the overall life-span and operational effectiveness of the printhead are reduced when these problems occur. Similar problems can take place if the printhead structure is incapable of withstanding the high-temperature conditions which can be encountered during sustained use. Temperature increases within a thermal inkjet printhead will normally result from selective energization of the thin-film heating resistors on the silicon substrate which takes place during printhead operation. Increases in printhead temperature can also be caused by extraneous heat radiating from adjacent operating components in the printer unit. Under these conditions, internal separation and/or structural deformation of various printhead components (e.g. the barrier layer, orifice plate, and the like) may take place which can cause a variety of problems. Specifically, chemical and/or thermal deterioration of the component layers in a thermal inkjet printhead can cause either total failure of the printhead or a continuous deterioration in print quality/resolution over time. In this regard, heat and solvent resistance (as well as a high degree of overall structural integrity) are important factors in producing a completed ink cartridge printhead having a long life-span which is capable of producing clear and distinct images over prolonged time periods.
Prior to development of the present invention, a need existed for an improved durability ink cartridge printhead having an orifice plate preferably manufactured from a non-metallic organic polymer composition. Likewise, a need generally remained for a printhead having a high level of structural integrity and chemical/thermal stability. The present invention satisfies these goals in a unique manner by providing an ink cartridge printhead with a specially-designed internal structure that is characterized by improved durability levels (e.g. ink-resistance and thermal stability). Accordingly, the claimed invention represents a substantial advance in ink printing technology as discussed in detail below.